I havent touched a Mack kingpin in 10 years and have 3 to work on this winter a 96 12k axle and 2ea 2003 18k axles. I think I have the tear down under control, but setting the lower nut I am looking for some specifications. As far as I can tell you snug the nut for the bottom bearing up tight and back it off till you get some clearance, similar to a tapered wheel bearing. Also looking for some verification of the direction of the seals.
you want a few thousandths up and down play when the spindle gets loaded. prepack the thrust bearing fefore you install it. I have always wiped a film of chassis grease on everything as I go together.Easiest to set with a dial indicator. set the nut to give about .005 up and down play. If you can swing the spindle freely both ways without it rubbing anywhere with just a little end play, you should be OK. It will gain a little clearance as the miles go by. Seals have the lips facing out so as to let the excess grease pass by while keeping water out.